Various instruments have found use for applications requiring level sensing of, for example, a liquid or bulk material in a vessel. Such instruments include float sensors, ultrasonic level sensors and capacitance-type level sensors. With any such instrument it is desirable that the instrument be reliable and provide repeatable measurements, as well as being simple to install and calibrate.
With a capacitance-type level sensor, the instrument includes a circuit connected to a probe adapted to be disposed in a material containing vessel. The probe exhibits capacitance. Capacitance increases as part of the probe is surrounded by material of dielectric constant greater than one. The capacitance present between the probe and the vessel can be measured to determine level of the material in the vessel.
A capacitance point level switch is operable to sense a specific level of the material in the vessel and provide a discrete output, such as with a relay contact, when the material is at a sufficient level to cause the capacitance between the probe and the reference to exceed the specific level. To assure accuracy, it is desirable that such levels be easily selected in the instrument.
The present invention is intended to satisfy the above requirements.